Evaporation crucible

ABSTRACT

An evaporation crucible which comprises a central tubular section which contains a longitudinal open slot. A plate is connected along one edge of the slot and extends at an angle within the tubular portion for a distance short of the inside wall of the tubular portion.

United States Patent 11 1 0111111 11 et al.

14 1 Jul' '2'4, 1973 EVAPORATION CRUCIBLE [75] Inventors: Anthony J. Ciultini, Rochester;

Joseph J. Galen, l79l Plank Rd.; Lloyd A. Relyea, both of Webster, all of N.Y.

[73] Assignee: Xerox Corporation, Stanford, Conn.

[22] Filed: Dec. 20, 1971 [211 Appl. No.: 209,607

[52] US. Cl. 432/263 [51] Int. Cl. F27b 21/04 [58] Field of Search 263/47, 48, 49;

[56] References Cited 7 UNITED STATES PATENTS 3,598,384 8/l97l Zucchinelli 266/39 5/1969 Hanson etal .Q ..263/48X 1/1971 12111011 263/48 Primary ExaminerJohn'J Camby Attorney-James J. Ralabate, Owen D. Maryama etalQ [57] ABSTRACT An evaporation crucible which comprises a central tubular section which contains a longitudinal open slot. A plate is connected along one edge of the slot and extends at an angle within the tubular portion for a distance short of the inside wall of the tubular portion.

4 Claims, 4 Drawing Figures Patented July 24, 1973 INVENTORS ANTHONY J. CIUF'FINI JOSEPH' J. 'GALEN BY LLOYD A. RELYEA ATTORNEY 1 EVAPORATION CRUCIBLE BACKGROUND OF THE INVENTION usually an important factor with respect to its final use.

The use of open boats and tube-type crucibles in vacuum evaporation is common throughout the art, and the instant invention comprises a novel crucible design which overcomes somev of the shortcomings of conventional crucibles. Generally, in the use of crucibles which have an open orifice, there is a straight line of sight path between the liquid surface of the evaporant material and the substrate surface which is to be coated. When bubbling of the evaporant liquid occurs, as it normally does during evaporation, droplets from the bubbling surface end up on the substrate and give rise to what is termed spit and spatter. This condition is undesirable in that it usually adversely affects the use of the final coated product. This problem is of particular concern informing thin photoconductive coatings on the surface of a metallic plate or drum which is to be used as a photosensitive member for producing images in the art of xerography. While applicable to other materials, the novel crucible of the presentinvention has particular utility for use in the evaporation of photoconductive materials such as selenium and selenium alloys onto a support member such a plate or drum.

In addition to the above problems, the use of opentypecrucibles reduces the geometric latitude in fixturing within the coater apparatus, and in particular to vacuum coating apparatus, because of the relatively long distances which are required between the crucible and substrate to be coated. In addition, the efficiency of open tube or boat crucibles is not as high as would be desired. 7

It is apparent from the basicc rueible designs of the prior art that if the geometric arrangement of the crucible to the coated substrate is suchthat the line of sight path from the evaporant liquid to be evaporated is eliminated, it would thereby greatly reduce the chance of spit andspatter surface defects in the final coated article. In addition, such a design would increase the geometric latitude of fixturing within the coating apparatus in that it would allow closer placement between the evaporating crucible and the surface to be coated. This closer placement between the crucible and'substrateto be coated also increases the overall efficiency of the evaporation cycle, and allows for greater uniformity in coating thickness.-

OBJECTS OF THE INVENTION It is, therefore, an object of this invention to provide a novel evaporation crucible.

It is another object of this invention to provide an evaporation crucible suitable for use in forming photoconductivc coatings. v It is a further object of this invention to provide an evaporation crucible which exhibits improved efficiency and quality over conventional evaporation crucibles.

SUMMARY OF THE INVENTION The foregoing objects and others are accomplished in accordance with this invention by providing a novel crucible design in. which the straight line of sight path from the evaporant material to the surface to be coated has been eliminated. The crucible of the present invention may be defined as a modified tube-type crucible having an open longitudinal slot and an internal plate member which functions to both contain the liquid evaporant and deflect the flow of. vapor to a substrate to be coated. The cross-sectional configuration of the crucible is roughly that of the letter G when the crucible is tilted at an angle.

BRIEF DESCRIPTION OF THE DRAWING FIG. 4 illustrates three suitable positions for use of the evaporation crucible of the present invention.

DETAILED DESCRIPTION OF THE INSTANT INVENTION FIG. 1 illustrates a tubular crucible 10 of the present invention having a cross-sectional configuration conforming to the letter G when the crucible is tilted at an angle. Crucible 10 has an outer metal tubular shell 11 having a longitudinal slot 12 at its top surface and a plate member 13 connected at one end to one edge of slot 12. Plate 13 extends at an angle within the internal diameter of tube 11. Each end of tube 11 is capped with an end plate 14 and 15. The bottom portion of the tube portion 11 of crucible 10 is normally sectioned by plates 16 into a plurality of separate compartments 17.

It has been found that by sectioning the bottom of the crucible, greater efficiency and more uniform coatings are produced.

FIG. 2 illustrates an end view of crucible 10, with the evaporant liquid 18 contained within the bottom portion of the crucible. I

Conventional prior art tube crucibles 20 and open boats 30, as illustrated in FIG. 3, have a'straight line of .sight path between the alloy liquid surface and the substrate surface 19 to be coated. In operation, the crucible of the instant invention effectively eliminates the straight lineof the vapor path and thereby greatly reduces the chance of spit and spatter defects on the coated surface.

FIG. 4 illustrates three suitable positions of use for the crucible of the instant invention. Positions (A), (B) and(C) illustrate three suitable positions of the crucible for use in evaporating metals or non-metals onto any suitable surface 21. The arrows in these figures indicate the vapor flow path from the evaporant surface to the substrate surface to be coated. It can be seen that plate member 13 functions to hold the liquid evaporant 18- within the crucible while simultaneously deflecting the vapor flow on an indirect path to the surface to be coated. Tests have shown that the crucible configuration of the present invention greatly reduces surface defects over the conventional evaporation vessels described above.

The crucibles of the instant invention are usually used with direct resistance heating in which a high current is passed through the crucible by means of electrical connections being maintained at each end of the crucible. Generally, therefore, these crucibles are normally made of metals, such as for example, stainless steel. The lighter the gauge of the material making up the crucible, the lower the current or power required for evaporation. Crucibles of the present invention have utility in evaporating metals or non-metals for any suitable use, but have particular utility for the formation of photoconductive coatings for use in xerography, and more specifically, for the deposition of selenium and selenium alloys onto a supporting substrate such as a metallic cylinder, drum or flat plate.

In order to demonstrate the efficiency of the crucible of the present invention, the following tests were car ried out: Two crucibles of the present invention each were used to coat 15 aluminum cylinders having a 15 inch circumference with a photoconductive seleniumarsenic alloy (0.35 percent arsenic 99.65 percent selenium by weight). The crucibles were each charged with 51 grams of pellets of the above selenium alloy and resistance heated. The evaporation coating was carried out in under a vacuum of Torr. with the crucibles spaced less than 1 inch from the rotating aluminum cylinder surface. Coating was carried out until a 60 micron coating of selenium-arsenic alloy was formed on the aluminum surface. The above evaporation cycle resulted in substantially defect free uniform alloy coatings and an evaporation efficiency of 92 percent (i.e.,

47 grams of the alloy ended up on the aluminum surface). The same evaporation cycle was then carried out using a conventional tube and open boat crucible. The coating efficiency for these crucibles dropped to 30 percent, and the number of surface defects increased considerably. In addition, these boats were required to be spaced 6 to 8 inches away from the aluminum surface during the evaporation cycle.-

Although various modifications and equivalent components have been stated in the above description of the preferred embodiments of this invention, other suitable materials such as those listed above, may also be used with similar results.

Other modifications and ramifications of the present invention would appear to those skilled in the art upon reading the disclosure. These are also intended to be within the scope of this invention.

What is claimed is:

1. An evaporation crucible comprising a central, tubular portion containing a longitudinal slot, a plate member connected at one edge of said slot and extending within said crucible to a distance short of the inside wall of said crucible; with said tubular portion further containing an end plate at each end.

2. The crucible of claim 1 in which at least one portion of the internal surface of the tubular portion is divided into a plurality of compartments by a series of equally spaced plates.

3. The crucible of claim 1 in which said crucible is constructed of metal.

4. The crucible of claim 1 in which the plate member is positioned at an angle to substantially obstruct the slot opening when the crucible is tilted at an angle. 

1. An evaporation crucible comprising a central, tubular portion containing a longitudinal slot, a plate member connected at one edge of said slot and extending within said crucible to a distance short of the inside wall of said crucible; with said tubular portion further containing an end plate at each end.
 2. The crucible of claim 1 in which at least one portion of the internal surface of the tubular portion is divided into a plurality of compartments by a series of equally spaced plates.
 3. The crucible of claim 1 in which said crucible is constructed of metal.
 4. The crucible of claim 1 in which the plate member is positioned at an angle to substantially obstruct the slot opening when the crucible is tilted at an angle. 